1. Field of the Invention
This invention relates to an orthodontic appliance which is made from an alloy of gold and platinum or other precious metal of suitable luster and hardness, and to a method for preparing such an orthodontic retainer.
2. Description of the Prior Art
Gold alloys and other precious metal alloys are widely used in restorative dentistry, for example, as fillings, crowns and bridges. In such applications, the precious metal alloy that is used in any such restorative dental device is selected basically for its functional characteristics, such as durability and compatibility with the interior portion of a tooth to which it is attached and, in any such application, the precious metal alloy dental device is generally not readily visible from a position away from the wearer. Hence, the visual characteristics of a restorative device formed from a precious metal alloy do not have much significance in the selection of the metal alloy that is used in the device.
In orthodontics, however, various types of devices, such as brackets and retainers, are affixed to the front surfaces of the teeth being treated and, especially in the case of front teeth, both upper and lower, these devices are quite visible to someone who is near to the user and who is looking toward the user when the mouth of the user is open. Nevertheless, such orthodontic brackets and retainers have heretofore been formed from materials which lack the aesthetic qualities of precious metals, including such non-metallic materials as acrylic plastic, as is disclosed in U.S. Pat. No. 3,345,745 (G. Muller) and in U.S. Pat. No. 3,303,565 (G. V. Newman), and non-precious metals, such as stainless steel, as is disclosed in U.S. Pat. No. 4,100,678 (K. Yatabe) and in U.S. Pat. No. 4,165,561 (F. R. Miller, et al). Ceramics, such as aluminum oxide, as is disclosed in U.S. Pat. No. 4,216,583 (J. M. Reynolds), have also been used for such purposes. One of the problems that must be overcome with respect to the use of precious metal alloys in the manufacture of orthodontic appliances is that such precious metal alloys have greater weight than their prior art counterparts, due to the high densities of such precious metal alloys. Thus, there is a problem of movement or drift of the orthodontic appliances on the tooth, due to gravity, while the adhesive that is used to bond the orthodontic appliance is curing or setting, since the tooth surface to which the appliance is being bonded is usually oriented in a substantially vertical direction. Additionally, due to the relative chemical inertness of such a precious metal alloy, their use in orthodontic devices involves a problem that was not encountered in organic orthodontic devices, such as acrylic brackets and retainers, namely the problem that there is no appreciable chemical bonding of the dental adhesive to the precious metal dental device. Thus, the bonding of the dental adhesive to the precious metal orthodontic device must be almost entirely physical or mechanical in nature.